Pigment Red 112 With Enhanced Dispersibility

ABSTRACT

The invention provides a process for preparing uncoated, readily dispersible C.I. Pigment Red 112 by azo coupling in a microreactor, which comprises precipitating the coupling component in an upstream microreactor and coupling the precipitated coupling component in finely divided form to the diazo component in a microreactor. 
     The C.I. Pigment Red 112 of the invention features low dispersion harshness in alkyd resin varnish, and a PCB content of below 25 ppm.

In order to incorporate a pigment as color-imparting component into apaint, a printing ink, a synthetic resin or a varnish, it must be veryfinely divided by dispersion in the respective application medium, aprocess which often entails much time and energy. In the course of thismechanical operation, agglomerates are broken apart and the surface ofthe pigment is wetted by the binder system. Only then is the pigmentable fully to develop its performance properties. Manufacturers ofcolored products prefer those pigments for which this dispersion effortis extremely low.

There are a whole range of different possibilities described as to howto prepare readily dispersible pigments. Dispersibility can be improvedby surface modification, surface treatment, surface coating, or thepresence of particular inert auxiliaries or reagents. Anotherpossibility is the production of flushing pastes, which are producedfrom an aqueous pigment presscake by displacing the water with binderssuch as alkyd resins, cellulose acetobutyrate, mineral oil or anyorganic, water-immiscible solvents. A further possibility is thefurnishing of prepared products which comprise a predispersed pigmentand are therefore much easier to incorporate into an application mediumthan is the dry pigment powder on which the product in question isbased.

DE-A-14 69 782 describes how treating the pigments with long-chainaliphatic amines makes them easy to disperse. For that purpose the aminein the form of its ammonium salt is mixed with the moist pigment andliberated in the form of the free amine by a modification to the pH.

EP-A-0 451 094 describes how a similar effect is achieved through thetargeted addition of azo dyes. In that case the coupling component isactually precipitated in the presence of the dye. The dye is presentthroughout the synthesis of the pigment and is likewise part of theformulation produced.

JP 09176514 describes how dispersibility is improved by giving pigmentsa fluorine aftertreatment.

EP 1 081 195 A2 describes how pigments are stabilized in the state offine division that obtains immediately post-synthesis by means ofenveloping the surface with polymer layers.

WO 2004/094540 describes how the energy input needed for sufficientdispersion of the pigment in the application medium can be reduced byaround 20% by means of surface coating. This is done by jacketing thepigment particles with (meth)acrylate copolymers containing aminegroups.

All of the abovementioned possibilities for enhancing dispersibility aretied up with additional costs for materials, additional mixingoperations or further worksteps in addition to the pigment synthesisitself. The additional additives used may, furthermore, undesirablyalter the performance properties apart from the enhanced dispersibility.Depending on the chemicals legislation, the resultant formulation may besubject to mandatory labeling. Flushing pastes and prepared products,moreover, are less universal in their possible uses, and are difficultto standardize. Furthermore, additional costs arise for measures tocounter bacterial and fungal infestation.

C.I. Pigment Red 112 is a Naphthol AS pigment which is widely used inindustry. Its coloristic properties mean that it has found broad use inprinting inks, varnishes, and paints.

Finely divided incorporation of an untreated C.I. Pigment Red 112 into abinder system can be accomplished only with a high dispersion effort. Ifthe aim is to save energy, then greater amounts of dispersing assistantare needed. These greater amounts, however, often lead to acorrespondingly great influence on other properties, mostly unwanted.

It was an object of the invention, therefore, to provide readilydispersible C.I. Pigment Red 112 without the need for use of auxiliariesor additives or for surface modification.

It has been found that the object of the invention can be achieved,surprisingly, through a new pigment synthesis by means of microreactiontechnology, as described in WO 2005/105927, for example. Differingtherefrom, however, the coupling component is not used in the form ofits solution, but is instead precipitated in an upstream microreactor.

The invention provides a process for preparing uncoated, readilydispersible C.I. Pigment Red 112 by azo coupling in a microreactor,which comprises precipitating the coupling component in an upstreammicroreactor and coupling the precipitated coupling component in finelydivided form to the diazo component in a microreactor.

The term “uncoated” refers to a pigment whose surface is free fromadditives or auxiliaries that cannot be washed off, and moreparticularly is free from polymer layers, such as the (meth)acrylatepolymers referred to in the prior art, for example.

The term “readily dispersible” refers to a pigment having a dispersionharshness of less than 45, as defined below.

The coupling component used for preparing C.I. Pigment Red 112 isN-(2-methylphenyl)-2-hydroxy-3-naphthoamide. The amine used to preparethe diazo component is 2,4,5-trichloroaniline.

In the process of the invention at least the precipitation of thecoupling component and the azo coupling are carried out in amicroreactor. Also possible is a combination of three reactors forprecipitating the coupling component, diazotizing the amine to thediazonium salt, and reacting the two components to give the azo pigment.The diazotization may take place under customary conditions, i.e., attemperatures between 0 and 15° C. and at a pH of between −1 and 1. Theprecipitated coupling component is reacted in finely divided form withthe diazo component. In one preferred version of the process, therefore,the coupling component, following its precipitation, is subjected to wetgrinding, in a ball mill or equivalent assembly, for example, until aparticle size of around 1 micrometer or less has been reached.

Microreactors which can be used are the devices and apparatus describedin WO2005/105927 A1.

A microreactor is constructed from a plurality of laminae which arestacked on one another and bonded to one another and whose surfaces bearmicromechanically created structures which interact to form reactionspaces for chemical reactions. The system contains at least onecontinuous channel which communicates with the inlet and the outlet.

The flow rates of the streams of material are limited by the apparatus,as for example by the pressures which result in dependence on thegeometry of the microreactor. It is desirable for the microreactorreaction to go to completion, but it is also possible to adjoin a delayzone to create a delay time where necessary. The flow rates areadvantageously between 0.05 ml/min and 5 l/min, preferably between 0.05and 500 ml/min, more preferably between 0.05 and 250 ml/min, and moreparticularly between 0.1 and 100 ml/min.

The microreaction system is operated continuously, and the quantities offluid which are mixed with each other are in the microliter (μl) tomilliliter (ml) range. Critical to the production of solids in thismicroreaction system are the dimensions of the microstructured regionswithin the reactor. The selected dimensions must be large enough forparticulate solids to pass through without problems, so that thechannels do not become clogged. The smallest clear width of themicrostructures ought to be about ten times larger than the diameter ofthe largest particulate solids. Furthermore, appropriate geometricdesign must be carried out to ensure that there are no dead water zones,such as dead ends or sharp corners, for example, where particulatesolids might settle. Preference is therefore given to continuous pathswith rounded corners. The structures must be small enough to exploit theintrinsic advantages of the microreaction technology, namely precisetemperature control, laminar flow, diffusive mixing, and low internalreaction volume.

The clear width of the solution- or suspension-ducting channels isadvantageously 5 to 10 000 μm, preferably 5 to 2000 μm, more preferably10 to 800 μm, more particularly 20 to 700 μm.

The clear width of the heat exchanger channels is guided primarily bythe clear width of the liquid- or suspension-ducting channels and isadvantageously less than or equal to 10 000 μm, preferably less than orequal to 2000 μm, more particularly less than or equal to 800 μm. Thelower limit for the clear width of the heat exchanger channels is notcritical and is at most constrained by the pressure increase of the heatexchanger fluid to be pumped and by the necessity for optimum supply orremoval of heat.

The dimensions of the microreaction system used are as follows:

heat exchanger structures: channel width about 600 μm, channel height:about 250 μm;

mixer and delay zone: channel width about 600 μm, channel height about500 μm.

The microreactor is preferably charged from above with all heatexchanger fluids and reactants. The product and the heat exchangerfluids are preferably likewise removed from above. The supply of thirdand fourth liquids involved in the reaction (e.g., buffer solutions),where necessary, is realized via a T-junction located directly upstreamof the reactor—in other words, one reactant at a time can be mixed inadvance with the buffer solution. The requisite concentrations and flowsare monitored preferably via precision piston pumps and acomputer-controlled regulation system. The reaction temperature ismonitored via integrated sensors and is monitored and controlled bymeans of the regulation system and a thermostat/cryostat.

The preparation of mixtures of input materials may also take placebeforehand, in micromixers or in upstream mixing zones. It is alsopossible for input materials to be metered in downstream mixing zones orin downstream micromixers or microreactors.

The system used here is manufactured from stainless steel; othermaterials, such as glass, ceramic, silicon, plastics or other metals,for example, can similarly be used.

The pigment synthesis of the invention proceeds preferably as follows:first of all the coupling component,N-(2-methylphenyl)-2-hydroxy-3-naphthoamide, is dissolved, preferablywith sodium hydroxide solution, preferably in aqueous solution or inmixtures of water and solvents, or in organic solvents, such as, forexample, alcohols having 1 to 10 carbon atoms, such as methanol,ethanol, n-propanol, isopropanol, butanols, such as n-butanol,sec-butanol, tert-butanol, pentanols, such as n-pentanol,2-methyl-2-butanol, hexanols, such as 2-methyl-2-pentanol,3-methyl-3-pentanol, 2-methyl-2-hexanol, 3-ethyl-3-pentanol, octanols,such as 2,4,4-trimethyl-2-pentanol, cyclohexanol; or glycols, such asethylene glycol, diethylene glycol, propylene glycol, dipropyleneglycol, or glycerol; polyglycols, such as polyethylene glycols orpolypropylene glycols; ethers, such as methyl isobutyl ether,tetrahydrofuran or dimethoxyethane; glycol ethers, such as monomethyl ormonoethyl ethers of ethylene glycol or propylene glycol, diethyleneglycol monomethyl ether, diethylene glycol monoethyl ether, butylglycols or methoxybutanol; ketones, such as acetone, diethyl ketone,methyl isobutyl ketone, methyl ethyl ketone or cyclohexanone; aliphaticacid amides, such as formamide, dimethylformamide, N-methylacetamide orN,N-dimethylacetamide; urea derivatives, such as tetramethylurea; orcyclic carboxamides, such as N-methylpyrrolidone, valerolactam orcaprolactam; esters, such as carboxylic acid C₁-C₆ alkyl esters, such asbutyl formate, ethyl acetate or propyl propionate; or carboxylic acidC₁-C₆ glycol esters; or glycol ether acetates, such as1-methoxy-2-propyl acetate; or phthalic or benzoic acid C₁-C₆ alkylesters, such as ethyl benzoate; cyclic esters, such as caprolactone;nitriles, such as acetonitrile or benzonitrile; aliphatic or aromatichydrocarbons, such as cyclohexane or benzene; or alkyl-, alkoxy-, nitro-or halo-substituted benzene, such as toluene, xylenes, ethylbenzene,anisole, nitrobenzene, chlorobenzene, o-dichlorobenzene,1,2,4-trichlorobenzene or bromobenzene; or other substituted aromatics,such as benzoic acid or phenol; aromatic heterocycles, such as pyridine,morpholine, picoline or quinoline; and also hexamethylphosphoramide,1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, and sulfolane. Saidsolvents may also be used as mixtures. It is preferred to usewater-miscible solvents.

The coupling component is subsequently precipitated by introducing thecoupler solution and the precipitant solution via two reactant ports ofthe microreactor, and mixing these two solutions in the reactor chamber.The precipitant solution is preferably an aqueous solution of an organicor inorganic acid, such as acetic acid, hydrochloric acid or sulfuricacid, for example, or a mixture of different acids. Precipitation takesplace preferably at temperatures between 0 and 20° C., more particularlybetween 5 and 10° C.

The azo coupling reaction takes place preferably in aqueous solution orsuspension, though it is also possible to use organic solvents, asrecited above, where appropriate in a mixture with water. The statedsolvents may also be used as mixtures. It is preferred to usewater-miscible solvents. Azo coupling takes place preferably attemperatures between 20 and 40° C., more particularly between 25 and 35°C.

Although not necessary, it is possible in the process of the inventionas well to use the auxiliaries that are used in the conventionalprocesses, such as, for example, surfactants, pigmentary andnonpigmentary dispersants, fillers, standardizers, resins, waxes,defoamers, antidust agents, extenders, shading colorants, preservatives,drying retarders, rheology control additives, wetting agents,antioxidants, UV absorbers, light stabilizers, or a combination thereof.The auxiliaries may be added at any desired point in time before, duringor after the reaction in the microreactor, all at once or in two or moreportions. The auxiliaries may be added, for example, directly to thesolutions or suspensions of the reactants, or else during the reaction,in liquid, dissolved or suspended form. The total amount of auxiliariesadded may be 0% to 40%, preferably 1% to 30%, more preferably 2.5% to25%, by weight, based on C.I. Pigment Red 112.

The inventively prepared C.I. Pigment Red 112 is notable for aparticularly low dispersion hardness attained by none of the synthesisprocesses known up until now.

The invention accordingly also provides an uncoated C.I. Pigment Red 112having a dispersion harshness in alkyd resin varnish of less than orequal to 45, preferably less than or equal to 40, more preferably lessthan or equal to 35, more particularly less than or equal to 25.

Additionally provided by the invention is an uncoated C.I. Pigment Red112 prepared by the process of the invention.

Dispersion harshness is a measure of the dispersibility of a pigment ina particular application medium. For example, EP1282666 B1 describes thedispersion harshness of pigments in LDPE plastics.

In the case of C.I. Pigment Red 112, the application medium ispreferably a paint or a varnish, and so the dispersion harshness isdetermined advantageously in an alkyd resin varnish.

Alkyd resins are synthetic hydrophobic polymers formed by esterificationof polyhydric alcohols with polyprotic acids with addition of oils orfatty acids. A polyhydric alcohol used is, in particular, glycerol,pentaerythritol or trimethylolpropane; a polyprotic acid used is, inparticular, a phthalic acid, usually in the form of phthalic anhydride,also isophthalic acid.

Oils are, for example, linseed oil, fish oil, soybean oil, cottonseedoil, sunflower oil, tall oil, which may comprise diunsaturated andpolyunsaturated fatty acids, such as 9,12,15-linolenic acid, forexample.

Alkyd resins are distinguished by the level (“length”) of the oilcontent or fatty acid content:

below 40% oil: short-oil; between 40% and 60% oil: medium-oil; above 60%oil: long-oil.

Oils which include a sufficient amount of diunsaturated orpolyunsaturated fatty acids are referred to as drying oils, thecorresponding alkyd resins as drying or else as air-drying alkyd resins.

Alkyd resins are available commercially, usually in dissolved form.Suitable solvents include the following: paint and varnish makers'spirit, xylene, ethylbenzene, ethyl acetate, butyl acetate, acetone,methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK),methoxypropanol, methoxypropyl acetate, methanol, ethanol, isopropanol,isomeric butanols, and mixtures thereof.

Pigmented alkyd resin varnishes generally have a pigment content of 5%to 35% by weight.

For the determination of the dispersion harshness in the pigmented (P.R.112) alkyd resin varnish, in accordance with the invention, a comparisonis made of the relative color strengths of alkyd resin varnish grinds at6 minutes and at ninety minutes of dispersing time, in accordance withthe following formula (FS=relative color strength):

${{Dispersion}\mspace{14mu} {harshness}} = {\left( {\frac{{FS}\left( {90\mspace{14mu} \min} \right)}{{FS}\left( {6\mspace{14mu} \min} \right)} - 1} \right) \cdot 100}$

The smaller the value of the dispersion harshness, the more readilydispersible the pigment.

In this test the pigment samples are admixed with a defined amount ofgrinding varnish (air-drying, long-oil alkyd resin varnish) anddispersed in a dispersing assembly, such as a paint shaker, for example,for 6 minutes and for 90 minutes, under otherwise identical conditions.

The grinding varnish is made up for example as follows:

about 15% by weight of C.I. Pigment Red 112, about 85% by weight ofalkyd resin solution.

The alkyd resin solution is composed for example of:

-   45.4% by weight solution (70% by weight in paint and varnish makers'    spirit) of a long-oil, air-drying alkyd resin based on soybean    oil/phthalic anhydride (62% by weight oil, 27% by weight phthalic    anhydride, remainder primarily pentaerythritol and/or glycerol);-   2.6% by weight siccative (Ca octoate), 10% strength by weight in    paint and varnish makers' spirit, e.g., Octa-Soligen Ca;-   2.8% by weight soya lecithin;-   49.2% by weight paint and varnish makers' spirit.

Long-oil, air-drying alkyd resins are available commercially, as forexample under the trade name Vialkyd® AS 673 h/70% White Spirit (Cytec).

Subsequently the dispersed grinding varnishes are diluted with furtheralkyd resin varnish and also with a white paint and homogenized, andthis system is drawn down onto a test chart and dried. The FS isdetermined colorimetrically in accordance with the CIELAB formula.

The values of dispersion harshness in accordance with the inventionrelate preferably to determination in an air-drying, long-oil alkydresin, more particularly in the grinding varnish composition describedabove.

The pigment prepared in accordance with the invention is notableadditionally for a very low PCB content of less than 25 ppm, preferablyless than 10 ppm.

The pigment prepared in accordance with the invention is also notablefor a very low residual coupler content of less than 1.0% by weight,preferably less than 0.70% by weight.

The P.R. 112 of the invention can be employed in principle to pigmentall high molecular mass organic materials of natural or syntheticorigin, such as plastics, resins, varnishes, especially metallicvarnishes, paints, electrophotographic toners and developers, electricalmaterials, color filters, and also liquid inks and printing inks.Particularly preferred are paints, varnishes, and printing inks.

In the examples below, per cent means per cent by weight, unlessindicated otherwise, and parts mean parts by weight.

Test Systems:

The dispersibility is assessed on the basis of the color strength in anair-drying alkyd resin system. For this purpose, 4.5 g of pigment areweighed out into a 150 ml plastic beaker together with 25.5 g ofgrinding varnish, consisting of 45.38% Vialkyd® AS 673 h/70% strength byweight in White Spirit, 2.58% Octa-Soligen® Ca, 10% strength by weightin paint and varnish makers' spirit [P&VMS], 2.82% soya lecithin and49.22% P&VMS 145/200, 85 g of glass beads (3 mm φ) are added, and thesystem is then dispersed with a dispersing assembly, a paint shaker, forexample, for 6 minutes in one case and for ninety minutes in one case.After dispersion has taken place, 60 g of siccatived let down mixture(LA4 Let Down Mixture 54%, Esser-Lacke), consisting of 77.14% Vialkyd AS673 h/70% WS, 0.90% Bykanol-N®, 2.80% Octa-Soligen Dryer 173 and 19.16%P&VMS 145/200, are weighed in and the mixture is homogenized.

The varnishes thus produced are each weighed out into a plastic beakertogether with white paint (e.g. LA4 White Lacquer 27%, Esser-Lacke)(approximately 155 seconds efflux viscosity, DIN cup, 4 mm nozzle),consisting of 27.00% titanium dioxide, 49.97% Vialkyd AS 673 h/70% WS,2.70% Bentone® 34, 10% in P&VMS, 0.70% Octa-Soligen Ca 10%, 5.12% P&VMS180/210, 11.53% P&VMS 145/200, 1.48% Bykanol-N, 1.50% Octa-Soligen Dryer173, in a ratio of 1:3.7 (siccatived let down mixture: white paint), andthis system is homogenized in a shaker machine.

Sample and comparative are drawn down alongside one another using afilm-drawing apparatus (e.g., Vertrieb Erichsen GmbH & Co. KG) onto atest chart, (e.g., Chromolux® 200 from Zanders Feinpapiere AG). Thecharts are dried at 60° C. for sixty minutes.

Evaluation takes place colorimetrically in accordance with the CIELABformula.

The polychlorinated biphenyls (PCB) content is determined as describedin the article by N. Sistovaris, U. Donges, B. Dudeck; J. High Res.Chrom. 1990(13), 547ff.

The residual coupler content of the pigment is determined by HPLC on asystem with a quaternary gradient pump, variable wavelength detector,column oven, with a flow rate of 1.5 ml/min at an oven temperature of40° C., with an observation wavelength of 240 nm, against methyl4-nitrobenzoate as internal standard. The column used may be, forexample, a Phenomenex® Luna 5 μm phenyl-hexyl, 150×4.6 mm. 0.05 g of thesample are admixed with 5 ml of internal standard, consisting of theaforementioned compound in solution in 100 ml of acetonitrile, andtreated with ultrasound for 5 minutes, then filtered and applied in anamount of 0.2 microliter to the column.

EXAMPLE 1

1.1) Preparation of the Diazonium Salt Solution of2,4,5-trichloroaniline:

250 parts of water are introduced and 40.3 parts of2,4,5-trichloroaniline are first stirred in homogeneously at roomtemperature and admixed with 193 parts by volume of 31% strengthhydrochloric acid. Cooling then takes place to 0° C. with ice.Diazotization is carried out with 29 parts by volume of 40% strengthsodium nitrite solution. The resulting diazonium salt solution isadmixed with a clarifying aid and then filtered into a receiver vessel.The excess nitrite is removed by addition of amidosulfonic acid, and thetemperature is held at 10° C. by external cooling.

1.2) Preparation of a Solution of Coupling Component (Naphthol):

190 parts of water and 28 parts by volume of 33% strength sodiumhydroxide solution, and also 1 part of an alkylsulfonate, are introducedat room temperature, and 60 parts ofN-(2-methylphenyl)-2-hydroxy-3-naphthoamide are added. The mixture isstirred until a clear solution is obtained (=solution 1). In a secondstock vessel, a mixture of 176 parts of water, 2 parts of analkylsulfonate and 32 parts by volume of 80% strength acetic acid isprepared and is adjusted to room temperature (=solution 2).

1.3) Precipitation of the Coupling Component in a Microreactor:

The coupler solution (solution 1) and the dilute acid (solution 2) arepumped at a flow rate of 6 ml/min into the respective reactant ports ofthe microreactor (type: Cytos from CPC-Systems, Frankfurt). Via theregulated heat exchanger circuit of the microreactor, a precipitationtemperature of 5° C. is set and maintained. The resulting precipitate,with a pH of 5, is collected in a receiver vessel and held at atemperature of 5° C. It is thus available for the subsequent azocoupling.

1.4) Provision of Dilute Sodium Hydroxide Solution for Regulating the pHDuring Azo Coupling:

150 parts of a water/ice mixture are mixed with 100 parts by volume of33% strength sodium hydroxide solution and held at 5° C. by means ofexternal cooling.

1.5) Azo Coupling in a Microreactor:

The diazonium salt solution and the coupler suspension are pumped at aflow rate of 8 ml/min into the respective reactant ports of themicroreactor (type: Cytos from CPC-Systems, Frankfurt). In order toensure the required pH of approximately 4.5 for azo coupling, the dilutesodium hydroxide solution described in 1.4) is metered into the couplerprecipitate a short way upstream of the reactor inlet. The sodiumhydroxide solution is likewise conveyed into the reactant feedline ofthe microreactor by means of a calibrated piston pump via a T-junction,at a flow rate of 6 ml/min. Attached to the heat exchanger circuit ofthe microreactor is a thermostat, which sets the desired reactiontemperature of 20° C. to 40° C. The coupled pigment suspension iscollected in a receiver vessel, drawn off under suction, washedsalt-free, and dried.

The dispersion harshness is 21, the residual coupler content is 0.56%,and the polychlorinated biphenyls content is 6 ppm.

EXAMPLE 2

Synthesis takes place as described in example 1, with step 1.3) beingfollowed by the grinding of the precipitated coupler using a Dispaxmill.

The dispersion harshness is 25, the residual coupler content is 0.69%,and the polychlorinated biphenyls content is 3 ppm.

COMPARATIVE EXAMPLE 1 (BASED ON EP 0 319 452 A2, EXAMPLE 16)

40.3 parts of finely crystalline 2,4,5-trichloroaniline are stirredovernight in a mixture of 200 parts of water, 0.5 parts of analkylsulfonate and 200 parts by volume of 30% strength hydrochloricacid. Following addition of ice to the resulting suspension of thehydrochloride, diazotization is carried out by rapid introduction of 29parts by volume of 40% strength sodium nitrite solution, followed by anhour of stirring. Subsequently the nitrite excess is destroyed withamidosulfonic acid and the diazonium salt solution is clarified.

In the coupling vessel, 60 parts ofN-(2-methylphenyl)-2-hydroxy-3-naphthoamide are dissolved at 85° C. in200 parts of water to which 28 parts by volume of 33% strength sodiumhydroxide solution have been added. Following the addition of one partof the sodium salt of an alkylsulfonic acid to the clear solution, 30parts by volume of glacial acetic acid are added at 5 to 10° C. Azocoupling takes place at 40 to 50° C. by running the nitrite-freediazonium salt solution into the suspension with the coupling componentover the course of 2 to 3 hours. This is followed by stirring at 40 to50° C. until reaction is complete, at which point the pigment is drawnoff under suction, washed salt-free with water, and dried. Thedispersion harshness is 52, the residual coupler content 3.80%.

COMPARATIVE EXAMPLE 2 (BASED ON WO 90/15844, EXAMPLE 4)

40 parts of 2,4,5-trichloroaniline are stirred overnight in a mixture of200 parts of water, 200 parts by volume of 30% strength hydrochloricacid and 0.5 part of a secondary alkanesulfonate. Following addition ofice, diazotization is carried out rapidly with 29 parts by volume of a40% strength aqueous sodium nitrite solution, followed by stirring withnitrite excess for 1 hour. The nitrite excess is then destroyed withamidosulfonic acid. The clarified diazonium salt solution is admixedwith 5 parts of methacrylamide.

In the coupling vessel, 59.6 parts ofN-(2-methylphenyl)-2-hydroxy-3-naphthoamide are dissolved in a mixtureof 400 parts of water and 28 parts by volume of 33% strength sodiumhydroxide solution at 80 to 85° C. 15 parts by volume of a 10% strengthsolution of the alkanesulfonate used before are added, followed bycooling to 5 to 10° C. with ice and then addition of 25 parts by volumeof glacial acetic acid, to precipitate the coupling component in finelydivided form. Azo coupling takes place at 15 to 25° C. by running of thenitrite-free diazonium salt solution into the suspension with thecoupling component over the course of 2 hours. In this procedure the pHis held at 4 to 4.5 by dropwise addition of 10% strength sodiumhydroxide solution. Following completion of coupling and customaryworkup, the pigment is obtained with a dispersion harshness of 50; theresidual coupler content is 2.97% and the polychlorinated biphenylscontent is 20 ppm.

COMPARATIVE EXAMPLE 3 (IN LINE WITH WO2005/105927 A1)

The coupler solution prepared in section 1.2) of example 1 is suppliedfor azo coupling, without precipitation, as described in section 1.5) ofexample 1. The constant pH of 5 that is needed for coupling is achievedthrough regulated metered addition of the dilute sodium hydroxidesolution described in section 1.4) of example 1. Following solventwashing and membrane purification in the same way as in WO2005/105927A1, example 1, the pigment is obtained with a dispersion harshness of46; the residual coupler content is 1.36% and the polychlorinatedbiphenyls content is 11 ppm.

1. A process for preparing uncoated, readily dispersible C.I. PigmentRed 112 by azo coupling in a microreactor, comprising the steps ofprecipitating the coupling component in an upstream microreactor andcoupling the precipitated coupling component in finely divided form tothe diazo component in a microreactor.
 2. The process as claimed inclaim 1, wherein the amine is diazotized to the diazonium salt in amicroreactor.
 3. The process as claimed in claim 1, wherein theprecipitated coupling component is subjected to wet grinding.
 4. Theprocess as claimed in claim 1, wherein the coupling component isprecipitated with an organic or inorganic acid.
 5. An uncoated C.I.Pigment Red 112 having a dispersion harshness in alkyd resin varnish ofless than or equal to
 45. 6. A C.I. Pigment Red 112 as claimed in claim5, having a dispersion harshness in alkyd resin varnish of less than orequal to
 40. 7. A C.I. Pigment Red 112 as claimed in claim 5, having adispersion harshness in alkyd resin varnish of less than or equal to 35.8. A C.I. Pigment Red 112 as claimed in claim 5, having a dispersionharshness in alkyd resin varnish of less than or equal to
 25. 9. Anuncoated C.I. Pigment Red 112 made in accordance with the process ofclaim
 1. 10. A C.I. Pigment Red 112 as claimed in claim 5, having a PCBcontent of less than 25 ppm.
 11. A C.I. Pigment Red 112 as claimed inclaim 5, having a PCB content of less than 10 ppm.
 12. A C.I. PigmentRed 112 as claimed in claim 5, having a residual coupler content of lessthan 1.0% by weight.
 13. A C.I. Pigment Red 112 as claimed in claim 5,having a residual coupler content of less than 0.70% by weight.
 14. Apigmented high molecular mass organic material of natural or syntheticorigin pigmented by the C.I. Pigment Red 112 as claimed in claim
 5. 15.The pigmented high molecular mass organic material of natural orsynthetic origin as claimed in claim 14, wherein the high molecular massorganic material of natural or synthetic origin is a pigment paintvarnish or printing ink.